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Web address:
http://www.sciencedaily.com/releases/2008/08/
080821163848.htm
Manes, Trains And Antlers Explained: How Showy Male Traits Evolved
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A vibrant peacock strutting his stuff. (Credit: iStockphoto/Jennifer Daley)
ScienceDaily (Aug. 22, 2008) — For Charles Darwin, the problem of the peacock's
tail, in light of his theory of natural selection, was vexing in the extreme.
Indeed, in 1860, writing to Asa Gray, his most ardent American champion, Darwin
confessed: "The sight of a feather in a peacock's tail, whenever I gaze at it,
makes me sick!"
In his struggle to explain why such extravagant and seemingly burdensome
features existed, the great English naturalist struck upon the idea of sexual
selection -- that showy traits such as the Peacock's ornamentation were an
advantage in the mating game that outweighed other disadvantages.
A team of Wisconsin scientists has turned from the question of why such male
traits exist to precisely how they evolved. They have worked out the molecular
details of how a simple genetic switch controls decorative traits in male fruit
flies and how that switch evolved. By extension, the work explains the
mechanics of how the male lion got his mane, how the bull moose acquired such
an impressive set of antlers and, yes, how the peacock got its magnificent tail.
Writing in the latest edition (Aug. 22, 2008) of the journal Cell, a team led
by University of Wisconsin-Madison molecular biologist Sean Carroll describes
the regulation and evolution of a genetic circuit in fruit flies that permits
the male to decorate its abdomen. The work also shows how the regulation of the
same genetic circuit in females represses such ornamentation.
"This study is about the how, not the why," says Carroll, a Howard Hughes
Medical Institute investigator and one of the world's noted evolutionary
biologists. "How can this trait be made in one gender and not the other?"
The question of the origins of secondary sexual characteristics -- traits other
than reproductive organs that are peculiar to one gender or another -- is one
that dominates modern evolutionary biology, says Thomas Williams, a UW-Madison
postdoctoral fellow who helped lead the study. "Males and females basically
have the same set of genes, so how do you specifically modify the activity of a
male's genes but not a female's genes?"
The answer, according to the new Cell report, resides in the genetic repression
of a protein in the male fruit fly that permits it to color the tail end of its
abdomen.
"The flies did not need new genes to make a new pattern," Carroll says. "They
just changed how males and females use a common set of genes."
The genetic switch that governs expression of the protein, Carroll notes, is
ancient and originally evolved for an entirely different purpose, but over time
mutations accumulated, perhaps in response to sexual selection, that drove the
evolution of male flies with more colorful derrieres.
"The switch existed for tens of millions of years because it had a different
job," says Carroll. "But it got remodeled. Evolution is a cumulative process.
You have this machinery and it's easy to add a bell or a whistle. With this
particular trait, it evolved by exploiting (genetic) information that was
already there to make male bodies different from female bodies."
According to Williams and Carroll, the study provided no evidence that the
ornamentation process ever occurred in females and was subsequently repressed.
"We have enough evidence to believe this evolved in a male-specific way," says
Carroll.
The same process, Carroll and Williams argue, is at play in animals from humans
and elephant seals to fish and beetles. There is a world of exaggerated traits
in animals and evolutionary biologists today, like Darwin 150 years ago, are
engaged by the question of what advantages they confer.
"These are the most rapidly evolving traits in evolution," Carroll explains.
"If female tastes change, these traits go away. There is no reinforcement.
"It's a tradeoff," Carroll concludes. "As long as the gain outweighs the cost,
the feature will survive. The fruit fly's color pattern is a paradigm for
understanding how to use the same sets of genes in different sexes to come up
with different features."
Adapted from materials provided by University of Wisconsin-Madison.
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
University of Wisconsin-Madison (2008, August 22). Manes, Trains And Antlers
Explained: How Showy Male Traits Evolved. ScienceDaily. Retrieved August 22,
2008, from http://www.sciencedaily.com /releases/2008/08/080821163848.htm
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